For a much better performance delivered by your T-Mobile Galaxy S3 SGH-T999, it’s best if you follow our tutorial on how to upgrade it to Android 4.3 Jelly Bean CyanogenMod 10.2 custom ROM.

And, since you will be able to grab this firmware, you should be told the following: no tutorial is ever complete if there’s no list of requirements around. Find the ones which work with this handset in the next paragraph.

After you are done reading about those requirements, you need to begin the guide which will upgrade your phone to a must-have tool.

How to flash CM10.2 on T-Mobile Galaxy S3

Begin the whole process by downloading both Google Apps package from this location and the Jelly Bean 4.3 CM10.2 Nightly build custom ROM (file name: cm-10.2-20130814-NIGHTLY-d2tmo.zip) on your notebook. Continue with the next tasks: connect the smartphone to your laptop with the phone’s USB cord and after that be sure to go to where the packages are stored.

Once you’ve reached the destination, move them from there to the handset’s SD card root. Then, if the phone is still turned on, power it off.

Disconnect it afterwards from your PC so that it’s easy to boot it into Recovery Mode via these steps: switch your Galaxy S3 SGH-T999 on while pressing and holding, together, Home, Volume Up and Power.

After the appropriate mode has been entered by your phone, you will need to move on to the next steps. Here is how they must look like: perform a wipe of the phone’s own system (the wipe should be a full one). For that to go smoothly, you need to begin like this: opt for Factory Reset/Wipe Data, confirm, go to the device’s Recovery Screen, opt for Wipe Cache Partition and finish by selecting Wipe Dalvik Cache.

Wait for all three actions to be performed by your Samsung T999 and make sure to opt for Install zip from SD card with “Power“. The same key should be used for the selection of Choose zip from SD card.

The CyanogenMod 10.2 .zip file that is inside the device’s SD card root must be accessed now. Do this by first using the buttons for Volume to locate this file; after that opt for it with “Power” and wait until a second screen pops up on the display. Confirm the flashing of the file.

Repeat the same actions to flash the Gapps package, as well. The installation will then begin. After it ends, you have to go to Go Back and make sure your handset reboots in the next few minutes.

The rebooting should be started with the “Restart” option; opt for the latter and then wait again till the Galaxy S3 T999 restarts into the Android 4.3 Jelly Bean CM10.2 Nightly custom firmware. And that is all.